1. Field of the Invention
The present invention (first aspect) relates to an inspection apparatus that inspects defects of a pattern formed on a surface of an inspection object, and specifically, to an inspection apparatus that captures secondary charged particles varying properties of a surface of an inspection object, forms image data, and inspects a pattern and the like formed on the surface of the inspection object on the basis of the image data at a high throughput, and an inspection method.
Furthermore, the present invention (second aspect) relates to an inspection apparatus that inspects a sample surface using an electron beam and, particularly, to an inspection apparatus that can inspect sample surfaces (front, rear and outer peripheral surfaces) at high sensitivity using an electron beam while preventing foreign matters from adhering to the sample surfaces.
2. Description of the Related Art
(First Aspect)
A conventional semiconductor inspection apparatus supports a 100 nm design rule and technologies. Samples as inspection objects are wafers, exposure masks, EUV masks, NIL (nanoimprint lithography) masks, and substrates; the samples have thus been varying. At present, apparatuses and technologies that support a design rule for samples with 5 to 30 nm are required. That is, it is required to support L/S (line/space) or hp (half pitch) nodes of 5 to 30 nm in a pattern. In the case where an inspection apparatus inspects such samples, it is required to achieve a high resolution.
Here, “samples” are exposure masks, EUV masks, nanoimprint mask (and templates), semiconductor wafers, substrates for optical elements, substrates for optical circuits and the like. The samples include samples with patterns and samples without patterns. The samples with patterns include samples with asperities and samples without asperities. Patterns are formed of different materials on the samples without asperities. The samples without patterns include samples coated with an oxide film and samples with no oxide film.
Problems of the conventional inspection apparatuses are summarized as follows.
A first problem is insufficient resolution and throughput. In a conventional art of a mapping optical system, the pixel size is about 50 nm, and the aberration is about 200 nm. Achievement of further high resolution and improvement of the throughput require reduction in aberration, reduction in energy width of irradiation current, a small pixel size, and increase in current intensity.
A second problem is that, in the case of SEM inspection, the finer the structure to be inspected, the more serious the throughput problem is. This problem occurs because the resolution of an image is insufficient if a smaller pixel size is not used. These points are caused because the SEM forms an image and inspects defects on the basis of edge contrast. For instance, in the case of a pixel size of 5 nm and 200 MPPS, the throughput is approximately 6 hr/cm2. This example takes a time 20 to 50 times as long as the time of mapping projection. The time is unrealistic for inspection.
(Second Aspect)
The electron beam inspection apparatus is used for irradiating a surface of a sample, such as a semiconductor wafer, with a primary electron beam, detecting secondary electrons emitted from the sample surface or mirror electrons to acquire an image of a sample surface, and performing inspections for defects on the sample surface, pattern evaluation or the like on the basis of the image.
A sample, such as a semiconductor wafer, is conveyed in an atmosphere and vacuum for inspection or processing. It has been known that if, during such conveyance, foreign matters, such as particles having a diameter of e.g. 100 nm or less, can be prevented from adhering to a sample surface and adherence of foreign matters that are to be killer defects on a pattern to the sample surface can be reduced, yields are largely improved. If killer defects are left as they are in processes of manufacturing semiconductors or LSIs, wiring widths and insulation resistance values become insufficient and significantly degrade performance. Accordingly, some processes, such as correction or failure determination, are required to address the killer defects.
In particular, an electron beam inspection apparatus can achieve highly accurate measurement and inspection results by reducing adhesion of foreign matters, such as particles generated by the apparatus, to a sample surface. Thus, a process of adhesion of foreign matters to a sample surface can be identified and improvement can be achieved. Accordingly, for instance, defects can be reduced in an exposure process.
Conventionally, in relation to conveyance of a sample, measures have been taken that prevent foreign matters, such as particles, from being generated as much as possible. For instance, for an atmosphere conveyance system for a sample, a high-functioning filter and a mini-environment having a downflow are provided. The atmosphere conveyance system is stored in the mini-environment. Furthermore, a sample is electrically neutralized by a neutralization device, thereby suppressing adhesion of particles to the sample surface. In a vacuum conveyance system for a sample, variation in pressure is controlled by a load lock. However, it is typically difficult to reduce fine-sized foreign matters, such as particles having a diameter of 100 nm or less.
In view of such problems, the applicant has already proposed a method of removing foreign matters on a sample surface; the method detects foreign matters on a sample surface, moves the sample in a horizontal direction, charges an absorption electrode arranged facing and close to the sample surface in the polarity different from the charging polarity of the foreign matters, and electrostatically absorbs approaching foreign matters onto the absorption electrode to thereby detect the foreign matters on the sample surface, and removes the foreign matters on the sample surface when the foreign matters are detected (see Japanese Patent Laid-Open No. 2009-4161 (Patent Document 4)).
Furthermore, a particle monitor has been proposed that causes a dust collecting electrode to actively collect particles suspended in a plasma processing apparatus, accumulates the particles using a quadrupole linear trap or the like to a specific site, and electrically detects the particles, or detects the particles using laser scattered light (see Japanese Patent Laid-Open No. 2010-56270 (Patent Document 5)).
As the design rule for LSIs has significantly become fine, the sizes of foreign matters, which should be prevented from adhering to a sample surface, become finer. Adhesion of foreign matters, such as particles generated by operation of an inspection apparatus and the like, has become a significant problem. Measures against the problem are required to be taken.
However, it is difficult for a conventional foreign matter adhesion preventing mechanism to prevent fine foreign matters, such as particles having a diameter of e.g. 100 nm or less, from adhering to a sample surface. In particular, in the case where a sample is arranged on a stage in a vacuum chamber or the like and the sample surface is inspected by an electron beam inspection apparatus, no consideration has been given to suppression of occurrence of foreign matters, such as particles from the apparatus itself.
The conventional art described in Patent Document 4 detects that foreign matters adhere to a sample surface, and subsequently removes the foreign matters from the sample surface, but cannot prevent the foreign matters from adhering to the sample surface. In the conventional art described in Patent Document 5, the dust collecting electrode is provided on, for instance, a distal end of the particle monitor, for collecting particles suspended in the plasma processing apparatus, but cannot prevent the particles from adhering to the sample surface.
Furthermore, in some cases, static electricity caused by an air flow when the vacuum chamber is evacuated charges foreign matters, such as particles, remaining in the vacuum chamber, the charged foreign matters, such as particles, are electrostatically attracted to the sample surface, which is to be inspected, thereby contaminating the sample surface. As to the conventional vacuum chamber used for inspecting a sample surface, no measures are taken against electrostatically attracting foreign matters, such as particles, remaining in the vacuum chamber to the sample surface, and such residues are removed by cleaning. It is thus strongly demanded that residues incapable of being removed by cleaning in the vacuum chamber be prevented from adhering to the sample surface.
The present invention has been made in view of the problems. A first object thereof is to provide a foreign matter adhesion preventing method that can prevent foreign matters from adhering to a sample surface as much as possible, and an electron beam inspection apparatus that can inspect a sample surface using an electron beam while preventing foreign matters from adhering to the sample surface as much as possible.
Furthermore, Japanese Patent Laid-Open No. 2005-235777 (Patent Document 6) describes a sample surface observation method using an electron beam inspection apparatus. This conventional method uses shades (gradation difference) in an image that occurs at portions of open defects and lacking defects. At the portions with defects including open defects and lacking defects, shades (gradation difference), which do not ordinarily occur in a normal portion, appear in an image. Accordingly, the conventional method adopts procedures that compare a wafer surface image acquired from a surface of a semiconductor wafer with an ordinary surface image (of a sample without defects), and determines that the portion concerned is an open defect or a lacking defect if shades, which do not ordinarily appear, are identified.
However, the observation method disclosed in Patent Document 6 has a problem in that the gradation difference in a portion to be observed in some cases of the structure, material and the like of a sample as an observation object is originally small, and it is sometimes difficult to detect lacking defects and open defects.
Furthermore, particularly on open defects, an image of a portion where open defects exist sometimes becomes thicker (more black) and sometimes becomes thinner (more white) than an image of a normal portion. There is thus a problem in that it is significantly difficult to detect defects and classify the types of defects.
In view of such a problem, the inventors have repeatedly discussed detection of defects on a wiring structure for the sake of providing a sample surface observation method that acquires a sample surface image where the gradation difference between a defect portion and a normal portion is large and the difference shades of gray is clear, and can easily detect defects. As a result, the inventors have come to regard that the problem of the sample surface observation method disclosed in Patent Document 6 resides in detection of lacking defects and open defects in the same condition at the same time, and proposed a novel sample surface observation method (see Japanese Patent Laid-Open No. 2009-87893 (Patent Document 7)).
Patent Document 7 discloses a sample surface observation method that irradiates, with an electron beam, a sample surface where wiring including insulation material and conductive material is formed, and detects electrons including information on the structure of the sample surface, thereby acquiring a sample surface image to observe the sample surface. In a situation where the insulation material and the conductive material have the same luminance in the sample surface image, this method irradiates the sample surface with an electron beam to thereby easily and securely detect portions other than the insulation material and the conductive material, and further detects, as open defects on the sample surface, points in the sample surface image where the insulation material and the conductive material have different luminances to thereby easily and securely detect the open defects.
Furthermore, Patent Document 7 discloses a sample surface observation method that irradiates a sample surface with an electron beam in a condition where the difference in luminance between insulation material and conductive material in a sample surface image is the maximum, and acquires a sample surface image allowing easy discrimination from peripheral portions of lacking defects to achieve easy and secure detection of the lacking defects, and moreover, sets the condition where the difference in luminance is the maximum in a mirror electron region where electrons including information on the sample surface structure become mirror electrons, thereby allowing lacking defects to be effectively detected.
Patent Document 1: International Publication No. WO2002/001596
Patent Document 2: Japanese Patent Laid-Open No. 2007-48686
Patent Document 3: Japanese Patent Laid-Open No. H11-132975
Patent Document 4: Japanese Patent Laid-Open No. 2009-4161
Patent Document 5: Japanese Patent Laid-Open No. 2010-56270
Patent Document 6: Japanese Patent Laid-Open No. 2005-235777
Patent Document 7: Japanese Patent Laid-Open No. 2009-87893